Fluorescence in situ hybridization (FISH) on peripheral blood smears for monitoring Philadelphia chromosome-positive chronic myeloid leukemia (CML) during interferon treatment: a new strategy for remission assessment

Multiplex acute leukemia cytosensing using multifunctional hybrid electrochemical nanoprobes at a hierarchically nanoarchitectured electrode interface

We have developed a robust, nanobiotechnology-based electrochemical cytosensing approach with high sensitivity, selectivity, and reproducibility toward the simultaneous multiplex detection and classification of both acute myeloid leukemia and acute lymphocytic leukemia cells. The construction of the electrochemical cytosensor involves the hierarchical assembly of dual aptamer-functionalized, multilayered graphene-Au nanoparticle electrode interface and the utilization of hybrid electrochemical nanoprobes co-functionalized with redox tags, horseradish peroxidase, and cell-targeting nucleic acid aptamers. The hybrid nanoprobes are multifunctional, capable of specifically targeting the cells of interest, amplifying the electrochemical signals, and generating distinguishable signals for multiplex cytosensing. The as-assembled electrode interface not only greatly facilitates the interfacial electron transfer process due to its high conductivity and surface area but also exhibits excellent biocompatibility and specificity for cell recognition and adhesion. A superstructured sandwich-type sensor geometry is adopted for electrochemical cytosensing, with the cells of interest sandwiched between the nanoprobes and the electrode interface. Such an electrochemical sensing strategy allows for ultrasensitive, multiplex acute leukemia cytosensing with a detection limit as low as ~350 cells per mL and a wide linear response range from 5 × 10(2) to 1 × 10(7) cells per mL for HL-60 and CEM cells, with minimal cross-reactivity and interference from non-targeting cells. This electrochemical cytosensing approach holds great promise as a new point-of-care diagnostic tool for early detection and classification of human acute leukemia and may be readily expanded to multiplex cytosensing of other cancer cells.

Fluorescence in situ hybridization methods and troubleshooting applied to fixed cell suspensions

A robust procedure for performing fluorescence in situ hybridization (FISH) is described, with tips for troubleshooting. FISH probes are now more reliable and there is a greater range commercially available. FISH is an essential part of the cytogeneticist's repertoire. It remains a powerful, complementary adjunct to karyotype studies, and knowledge of the underlying chromosome abnormalities can be essential for understanding the FISH signal patterns.

Chronic myeloid leukemia: a prospective comparison of interphase fluorescence in situ hybridization and chromosome banding analysis for the definition of complete cytogenetic response: a study of the GIMEMA CML WP

In chronic myeloid leukemia, different methods are available to monitor the response to therapy: chromosome banding analysis (CBA), interphase fluorescence in situ hybridization (I-FISH), and real-time quantitative polymerase chain reaction (RT-Q-PCR). The GIMEMA CML WP (Gruppo Italiano Malattie Ematologiche Adulto Chronic Myeloid Leukemia Working Party) has performed a prospective study to compare CBA and I-FISH for the definition of complete cytogenetic response (CCgR). Samples (n = 664) were evaluated simultaneously by CBA and I-FISH. Of 537 cases in CCgR, the number of positive nuclei by I-FISH was less than 1% in 444 cases (82.7%). Of 451 cases with less than 1% positive nuclei by I-FISH, 444 (98.4%) were classified as CCgR by CBA. The major molecular response rate was significantly greater in cases with I-FISH less than 1% than in those with I-FISH 1% to 5% (66.8% vs 51.6%, P < .001) and in cases with CCgR and I-FISH less than 1% than in cases with CCgR and I-FISH 1% to 5% (66.1% vs 49.4%, P = .004). I-FISH is more sensitive than CBA and can be used to monitor CCgR. With appropriate probes, the cutoff value of I-FISH may be established at 1%. These trials are registered at http://www.clinicaltrials.gov as NCT00514488 and NCT00510926.

Utility of peripheral blood dual color, double fusion fluorescentin situhybridization forBCR/ABLfusion to assess cytogenetic remission status in chronic myeloid leukemia

The molecular signature of BCR-ABL fusion in chronic myeloid leukemia (CML) provides a unique tool for diagnosis and monitoring of tumor burden during therapy. The gold standard in this regard is conventional bone marrow cytogenetics. Peripheral blood fluorescent in situ hybridization (FISH) offers the possibility of a less invasive, more practical alternative method in terms of both cost and turnaround time. In the present study, we examined 296 paired samples from 65 patients with CML and demonstrate a tight correlation, in quantifying BCR-ABL burden between bone marrow cytogenetics, bone marrow dual color, double fusion (D-FISH), and peripheral blood D-FISH (P < 0.0001 for each). Furthermore, we demonstrate that peripheral blood D-FISH can be used as a surrogate for cytogenetic studies in monitoring cytogenetic remission status.

Automated detection of residual cells after sex-mismatched stem-cell transplantation - evidence for presence of disease-marker negative residual cells

BACKGROUND

A new chimerism analysis based on automated interphase fluorescence in situ hybridization (FISH) evaluation was established to detect residual cells after allogene sex-mismatched bone marrow or blood stem-cell transplantation.Cells of 58 patients were characterized as disease-associated due to presence of a bcr/abl-gene-fusion or a trisomy 8 and/or a simultaneous hybridization of gonosome-specific centromeric probes. The automatic slide scanning platform Metafer with its module MetaCyte was used to analyse 3,000 cells per sample.

RESULTS

Overall 454 assays of 58 patients were analyzed. 13 of 58 patients showed residual recipient cells at one stage of more than 4% and 12 of 58 showed residual recipient cells less than 4%, respectively. As to be expected, patients of the latter group were associated with a higher survival rate (48 vs. 34 month). In only two of seven patients with disease-marker positive residual cells between 0.1-1.3% a relapse was observed. Besides, disease-marker negative residual cells were found in two patients without relapse at a rate of 2.8% and 3.3%, respectively.

CONCLUSION

The definite origin and meaning of disease-marker negative residual cells is still unclear. Overall, with the presented automatic chimerism analysis of interphase FISH slides, a sensitive method for detection of disease-marker positive residual cells is on hand.

Fluorescent in situ hybridization in the diagnosis, prognosis, and treatment monitoring of chronic myeloid leukemia

The unique molecular characteristic of chronic myeloid leukemia (CML), the disease-causing ABL (9q34) to BCR (22q11) translocation, has provided an invaluable tool for disease diagnosis and monitoring of treatment response. The traditional standard in this regard is bone marrow karyotype, also known as conventional cytogenetics (CC), which reveals a shortened chromosome 22, the Philadelphia chromosome, t(9;22)(q34;q11). CC in CML has also been effectively used for monitoring the response to drug therapy. However, this particular laboratory test misses submicroscopic BCR/ABL translocations and is suboptimal for minimal residual disease (MRD) assessment. Both fluorescence in situ hybridization (FISH) and reverse-transcriptase polymerase chain reaction (RT-PCR) feature higher sensitivity in terms of both diagnosis and MRD assessment in CML, compared to CC. Another advantage of these alternative tests is their effective applicability to peripheral blood specimens. The current review highlights the practical literature with respect to the use of FISH for CML whereas the use of RT-PCR has been extensively covered in recent communications.

Detection and monitoring of minimal residual disease by quantitative real-time PCR

BACKGROUND

The detection of malignant cells by quantitative real-time PCR has become state of the art for diagnosis, monitoring response to treatment and detection of minimal residual disease (MRD) in patients with leukemia or lymphoma. In order to be used in high-throughput analyses technical details have to be standardized to improve reproducibility and comparability of quantitative results obtained in different laboratories.

METHODS

Molecular monitoring of disease activity during and after treatment based on the detection of malignant cells in circulation or bone marrow by quantitative real-time PCR will be helpful to develop individualized treatment strategies for every patient.

CONCLUSIONS

The effectiveness of any kind of innovative treatment with specific antibodies, cellular immunotherapy or molecules designed for specific targets of tumor cells can be controlled at a very high level of sensitivity and accuracy. Based on quantitative results indicative for success or treatment failure, therapeutic changes upon the detection of progressive disease at the molecular level can be made even before symptoms or signs of clinical relapse occur. Hopefully, this will lead to higher cure rates and improved long-term survival.

Wt1 is not essential for hematopoiesis in the mouse

WT1 has been implicated in human leukemia and hematopoiesis, but its role in stem cell differentiation is not yet fully defined. We show that Wt1-null murine fetal liver cells are capable of reconstituting functional hematopoiesis following transplantation into irradiated recipients. There was also no significant difference between the in vitro colony-forming ability of wild-type and Wt1-null cells. Using a reporter gene assay in a transgenic mouse system, expression from the WT1 promoter was detectable in adult bone marrow, but undetectable in subsets of different hematopoietic cells. We conclude that Wt1 is not essential for murine hematopoiesis and that there may be significant differences in its role between mouse and man.

Fluorescence In Situ Hybridization Monitoring of BCR-ABL-Positive Neutrophils in Chronic-Phase Chronic Myeloid Leukemia Patients during the Primary Stage of Imatinib Mesylate Therapy

We describe a method for monitoring chronic myeloid leukemia (CML) patients treated with imatinib that uses fluorescence in situ hybridization (FISH) to detect BCR-ABL in peripheral blood (PB) granulocytes. First, we compared this method, termed Neutrophil-FISH, with interphase FISH (i-FISH) analysis of bone marrow (BM), i-FISH analysis of PB mononuclear cells, and conventional cytogenetic analysis (CCA) of BM in 30 consecutive CML patients. We found the percentage of BCR-ABL-positive neutrophils as determined by Neutrophil-FISH to correlate best with the percentage of Philadelphia chromosome-positive metaphases in the BM determined by CCA (y = 0.8818x + 5.7249; r(2) = 0.968). We then performed a serial Neutrophil-FISH study of 10 chronic-phase CML patients treated with imatinib and found that the technique could clearly separate imatinib responders from nonresponders within 12 weeks of drug administration. There was a significant difference in the percentages of BCR-ABL-positive neutrophils between responder (mean 3 SD, 18.2% 3 11.8%) and nonresponder (82.4% 3 5.1%) groups at 12 weeks (P < .0001, Student t test).Together with real-time quantitative polymerase chain reaction analysis, Neutrophil-FISH represents another useful method for monitoring CML patients during the primary myelosuppressive stage of imatinib therapy because it is a quick, simple, and reliable method for assessing cytogenetic response.

Chronic myeloid leukemia: current application of cytogenetics and molecular testing for diagnosis and treatment

Chronic myeloid leukemia provides an illustrative disease model for both molecular pathogenesis of cancer and rational drug therapy. Chronic myeloid leukemia is a clonal stem cell disease caused by an acquired somatic mutation that fuses, through chromosomal translocation, the abl and bcr genes on chromosomes 9 and 22, respectively. The bcr/abl gene product is an oncogenic protein that localizes to the cytoskeleton and displays an up-regulated tyrosine kinase activity that leads to the recruitment of downstream effectors of cell proliferation and cell survival and consequently cell transformation. Such molecular information on pathogenesis has facilitated accurate diagnosis, the development of pathogenesis-targeted drug therapy, and most recently the application of molecular techniques for monitoring minimal residual disease after successful therapy. These issues are discussed within the context of clinical practice.

Chronic myeloid leukemia: pathophysiology, diagnostic parameters, and current treatment concepts

Chronic myeloid leukemia (CML) is a stem cell disease characterized by excessive accumulation of clonal myeloid (precursor) cells in hematopoietic tissues. CML cells display the translocation t(9; 22) that creates the bcr/abl oncogene. The respective oncoprotein (= BCR/ABL) exhibits constitutive tyrosine kinase activity and promotes growth and survival in CML cells. Clinically, CML can be divided into three phases: the chronic phase (CP), the accelerated phase (AP), and the blast phase (BP) that resembles acute leukemia. Progression to AP and BP is associated with occurrence of additional genetic defects that cooperate with bcr/abl in leukemogenesis and lead to resistance against antileukemic drugs. The prognosis in CML is variable depending on the phase of disease, age, and response to therapy. The only curative approach available to date is stem cell transplantation. For those who cannot be transplanted, the BCR/ABL tyrosine kinase inhibitor STI571 (Glivec, Imatinib), interferon-alpha (with or without ARAC), or other cytoreductive drugs are prescribed. Currently available data show that STI571 is a superior compound compared to other drugs in producing complete cytogenetic and molecular responses. However, despite superior initial data and high expectations for an effect on survival, long term results are not available so far, and resistance against STI571 has been reported. Forthcoming strategies are therefore attempting to prevent or counteract STI571 resistance by co-administration of other antileukemic drugs. Whether these strategies will lead to curative drug therapy in CML in the future remains at present unknown.

FISH for BCR-ABL on interphases of peripheral blood neutrophils but not of unselected white cells correlates with bone marrow cytogenetics in CML patients treated with imatinib

Interphase fluorescence in situ hybridization (I-FISH) for the BCR-ABL translocation performed on peripheral blood (PB) white cells has been suggested as a surrogate for conventional bone marrow (BM) cytogenetics for monitoring patients with chronic myeloid leukemia (CML). I-FISH is faster, less costly, and does not require BM aspiration. For patients treated with interferon-alpha (IFN), a good correlation between the two methods has been demonstrated in several though not all studies. However, imatinib mesylate (STI571) has largely replaced IFN as the standard drug treatment for CML, raising the question if the results obtained in IFN-treated patients are applicable to patients on imatinib. We therefore compared the two methods in patients on imatinib and patients on other therapies, mainly IFN (collectively referred to as nonimatinib therapies). Our results demonstrate that the correlation between I-FISH and cytogenetics is much weaker in patients on imatinib than in patients on nonimatinib therapies. Correction of the I-FISH values for the proportion of lymphocytes barely improved the correlation, probably as a result of unpredictable proportions of Philadelphia-positive B cells. By contrast, I-FISH of PB neutrophils was much better correlated with BM cytogenetics. We conclude that I-FISH on unselected PB white cells is not suitable for monitoring patients on imatinib.

Monitoring bcr-abl by polymerase chain reaction in the treatment of chronic myeloid leukemia

The elucidation of the molecular biology of chronic myeloid leukemia (CML) has provided a paradigm for understanding leukemogenesis, targeted drug development, and disease monitoring at the molecular level. Minimal residual disease (MRD) monitoring by fluorescence in situ hybridization and polymerase chain reaction (PCR) has become an important tool in predicting relapse after allogeneic transplant, allowing for early intervention strategies such as donor lymphocyte infusion. MRD monitoring is important for assessment of disease status in patients who obtain a complete cytogenetic remission, and this approach is likely to play an important role in following patients to determine who will relapse on imatinib mesylate therapy. This review focuses primarily on MRD monitoring by PCR.

Fluorescence in situ hybridization BCR/ABL fusion signal rate in interphase nuclei of healthy volunteer donors: a test study for establishing false positive rate

Fluorescence in situ hybridization (FISH) using chromosome-specific DNA probes is rapidly becoming a part of clinical laboratory practice. However, as a relatively new clinical test, it is not yet standardized and for practical reasons each laboratory must establish its own criteria. For this purpose we have evaluated the specificity of a dual-color BCR/ABL translocation probe by establishing the range of BCR/ABL fusion-positive scores in a healthy donor group. The false positive rate (FPR), determined by the percent of FISH BCR/ABL fusion-positive cells found in the specimens of healthy donors, was estimated at 2.3% (mean = 1%-4%). Thus the cut-off value for false positive nuclei was set at 5%.

Correlation between BCR-ABL expression and tumor burden is restricted to the transition from minor to major cytogenetic response in interferon treated CML patients

The interferon treatment of chronic myeloid leukaemia has been monitored by investigating the tumour burden as revealed by fluorescence in situ hybridization and the expression of BCR-ABL chimera determined by quantitative reverse transcription polymerase chain reaction. These parameters were obtained from the peripheral blood of 51 untreated and 104 follow-up patient samples. Poor correlation (r=0.31) was found between BCR-ABL expression and tumor load in all samples as well as in untreated patients, and this correlation was even less in all follow-up cases (r=0.28). Regarding chimera expression five order of magnitude difference existed in the untreated patients and this value dropped to two in those with complete cytogenetic response. Only the major and the complete cytogenetic response groups differed significantly (p<0.001) in the BCR-ABL expression from that of patients at diagnosis. Among the different cytogenetic response groups the only significant difference (p<0.01) in the BCRABL expression was obtained between the major and the minor responders. In the individual patients not only correlated changes of residual tumour mass and chimera expression, but mainly independent changes of these two parameters were observed. This indicates that the BCR-ABL expression and the tumor burden are largely independent variables.

Efficiency of interphase fluorescence in situ hybridization for BCR/ABL on peripheral blood smears for monitoring of CML patients: a comparison with bone marrow findings

Conventional cytogenetic analysis (CCA) is the standard method for monitoring of the Philadelphia (Ph) chromosome in chronic myeloid leukemia (CML). Evaluation of breakpoint cluster region/abelson murine leukemia (BCR/ABL) fusion using interphase fluorescence in situ hybridization on peripheral blood smears (PB-FISH) might be another approach allowing more frequent and less invasive follow-up investigations. Herein, BCR/ABL fusion gene was assessed on 21 PB smears from 16 CML patients in chronic phase. Results of PB-FISH were compared with those of CCA and interphase FISH on bone marrow aspirates (BM-FISH). PB-FISH analysis was combined with CD3 immunophenotyping that allowed simultaneous investigation of the leukemic status of CD3(+) T lymphocytes and scoring CD3(-) cells for BCR/ABL fusion gene. Moreover, the frequency of BCR/ABL fusion in nonlymphoid PB cells was estimated according to the differential leukocyte counts. The incidence of BCR/ABL(+) fusion signals in CD3(+) T cells of CML patients was 5.3% (SD +/- 1.9) and did not exceed the normal cut-off value of 8%. A significant correlation (P < 0.001) was found between results of PB-FISH and methods of BM analysis (CCA or BM-FISH). Correction of PB-FISH results to include only nonlymphoid or CD3(-) cells reduced the mean of differences and improved agreement between PB-FISH and CCA or BM-FISH methods. The best agreement was noted between CCA and PB-FISH on nonlymphoid cells. On the other hand, results of BM-FISH agreed well with those of PB-FISH on CD3(-) cells. These findings imply that PB-FISH on nonlymphoid or CD3(-) cells is reliable and may replace BM analysis for monitoring of response to treatment in CML patients.

Detection of the BCR-ABL gene by interphase fluorescence in situ hybridization (iFISH) in chronic myelogenous leukemia patients after hemopoietic stem cell transplantation: the feasibility of iFISH monitoring of therapeutic response in peripheral blood

The detection of the Philadelphia (Ph) translocation has been accomplished primarily by cytogenetic analysis and reverse transcriptase polymerase chain reaction (RT-PCR). RT-PCR is highly sensitive (1/10(4)-10(6)) but not quantitatively reliable and is thus unsuitable for the monitoring of Ph-positive cells during therapy. Interphase fluorescence in situ hybridization (iFISH) allows analysis of a large number of cells (> 500) in a timely and efficiently quantitative manner. We obtained 118 peripheral blood (PB) and 127 bone marrow (BM) samples from 75 adult chronic myelogenous leukemia (CML) patients undergoing stem cell transplantation. We simultaneously performed nested RT-PCR and iFISH for all samples. False-positive cells were detected in 2.48% +/- 0.93% (mean +/- SD) of PB samples and 2.75% +/- 0.83% of BM samples. The iFISH results for PB and BM ranged from 1.4% to 92.8% and 1.0% to 93.8%, respectively. Correlation analysis of iFISH results for PB versus BM samples showed a strong relation (r = .993). A significant correlation (P < .05) was also found between iFISH and first-round RT-PCR. The sensitivity of BCR-ABL iFISH was similar to that of first-round RT-PCR, and iFISH results for PB and BM were also well correlated. Thus, iFISH analysis of PB and/or BM samples may be more clinically reliable than RT-PCR in the quantitative monitoring of BCR-ABL fusion in CML after transplantation.

Comprehensive comparison of FISH, RT-PCR, and RQ-PCR for monitoring the BCR-ABL gene after hematopoietic stem cell transplantation in CML

The reverse transcriptase-polymerase chain reaction (RT-PCR) was compared with fluorescence in situ hybridization (FISH) and real-time quantitative RT-PCR (RQ-PCR) for minimal residual disease (MRD) monitoring in 266 post-transplant bone marrow samples from 78 patients with chronic myelogenous leukemia (CML). The sensitivities of FISH to BCR-ABL positive samples determined by first-round (1st) RT-PCR, second-round (2nd) RT-PCR, and RQ-PCR were 64.2%, 25.8%, and 20.7%, respectively. The BCR-ABL/ABL ratio by RQ-PCR had a mean of 0.000 13 in the 1st RT-PCR-negative samples and 1.42 in the 1st RT-PCR-positive samples (P<0.001), and means of 0.000 39 and 0.51 in the 2nd RT-PCR-negative and -positive samples (P< 0.001). The mean ratios of BCR-ABL/ABL by RQ-PCR were significantly different in N/N (1st/2nd RT-PCR) or N/P and P/P (P<0.001), but not in N/N and N/P, which showed that the discriminative power of RQ-PCR is confined to the 1st RT-PCR level. In this respect, monitoring of the 1st RT-PCR might be useful for estimating normalized BCR-ABL levels after transplantation. Nested RT-PCR was of limited use, as RQ-PCR quantified the BCR-ABL transcripts in 60 (91%) of 66 samples determined to be negative by 2nd RT-PCR. FISH was significantly correlated with RQ-PCR in FISH-positive samples (n=24, r=0.79, P=0.001). An increase of FISH preceded that of RQ-PCR in a few cases with molecular relapse. By analyzing a large number of samples post-transplant, we found that RQ-PCR might be the most useful assay for MRD monitoring; however, FISH and RT-PCR were found to be useful complementary tools.

Detection of minimal residual disease

A high percentage of patients with leukemia, lymphoma, and solid tumors achieve a complete clinical remission after initial treatment, but the majority of these patients will finally relapse from residual tumor cells detectable in clinical remission only by the most sensitive methods. The in vitro amplification of tumor-specific DNA or RNA sequences by polymerase chain reaction (PCR) allows identification of a few neoplastic cells in 10(4) to 10(6) normal cells. Depending on the underlying malignant disease and therapeutic treatment, the presence of residual tumor cells in an individual patient may herald relapse, but a long-term stable situation or slowly vanishing tumor cells are also possible. Molecular monitoring of residual leukemia and lymphoma cells by quantitative PCR techniques has provided important information about the effectiveness of treatment and the risk of recurrent disease as shown by minimal residual disease (MRD) analysis in patients with various malignant diseases. Such diseases include childhood acute lymphoblastic leukemia, after induction therapy; acute promyelocytic leukemia, during and after chemotherapy; and chronic myelogenous leukemia, during treatment with alpha-interferon and after allogeneic bone marrow transplantation. Evaluation of the predictive value of the detection of MRD has to take into account its evolution and course, the pathogenesis, biology, and natural course of the underlying malignant disease, the molecular genetic lesion, and finally, the type of treatment. Quantification of minimal residual cells by the recently developed real-time quantitative PCR technique will surely have a major impact on our therapeutic strategies for patients with leukemia, lymphomas, and solid tumors. Based on quantitative PCR data, the terms molecular remission and molecular relapse have to be exactly defined and validated in prospective clinical trials to assess the biological and clinical significance of MRD in various types of malignancies.

Comparison of chromosome banding analysis, interphase- and hypermetaphase-FISH, qualitative and quantitative PCR for diagnosis and for follow-up in chronic myeloid leukemia: a study on 350 cases

For the diagnosis of CML and for monitoring of treatment response the detection of the t(9;22)(q34;q11) or the BCR-ABL rearrangement is necessary. Chromosome banding analysis (CA) is still the gold standard but other techniques like Southern blot, fluorescence in situ hybridization (FISH) and polymerase chain reaction (PCR) are available. We analyzed 350 CML patients at different stages of disease in parallel with CA, interphase-FISH (IP-FISH), hypermetaphase-FISH (HM-FISH) and RT-PCR. In 20 cases with no Ph(+) metaphases in CA, HM-FISH detected 0.2 to 10% BCR-ABL(+)metaphases. After IP-FISH 107 samples were judged as negative. However, in 17 of these samples HM-FISH detected BCR-ABL(+) metaphases (0.3-11%), and in eight cases CA detected Ph(+) metaphases (2.5-25%). A comparison of IP-FISH performed on uncultivated cells vs cells cultivated for 48 h in 70 cases revealed a higher proportion of BCR-ABL+ cells in the cultivated samples. If nested PCR was negative, all other methods were negative in all cases too. In addition, 94 cases were evaluated using real-time PCR (LightCycler technology). The BCR-ABL/cABL ratio measured showed a high correlation with all other methods. Interestingly, a wide range in the BCR-ABL/ABL ratio was observed especially in patients who showed 100% Ph-positive metaphases in CA. In conclusion, CA, IP-FISH, HM-FISH and real-time PCR give reliable results but differences due to measurement of different target structures have to be kept in mind when using these data for definition of remission status.

Chronic myelogenous leukemia: laboratory diagnosis and monitoring

Rapid developments have occurred both in laboratory medicine and in therapeutic interventions for the management of patients with chronic myelogenous leukemia (CML). With a wide array of laboratory tests available, selecting the appropriate test for a specific diagnostic or therapeutic setting has become increasingly difficult. In this review, we first discuss, from the point of view of laboratory medicine, the advantages and disadvantages of several commonly used laboratory assays, including cytogenetics, fluorescence in situ hybridization (FISH), and qualitative and quantitative reverse transcriptase-polymerase chain reaction (RT-PCR). We then discuss, from the point of view of clinical care, the test(s) of choice for the most common clinical scenarios, including diagnosis and monitoring of the therapeutic response and minimal residual disease in patients treated with different therapies. The purpose of this review is to help clinicians and laboratory physicians select appropriate tests for the diagnosis and monitoring of CML, with the ultimate goal of improving the cost-effective usage of clinical laboratories and improving patient care.

Cytogenetics of chronic myeloid leukaemia

The standard Philadelphia (Ph) translocation t(9;22), its variants and a proportion of Ph-negative cases are positive for the BCR-ABL fusion gene, as determined by molecular analysis. Extensive deletions of chromosome 9 and 22 derived sequences around the translocation breakpoints on the derivative 9 are seen in 10-30% of patients at diagnosis and may confer a worse prognosis. Additional cytogenetic changes can occur in the few months before or during disease progression and are often specific for blast morphology; however, the molecular basis of the most common additional cytogenetic abnormalities is largely unknown. Cytogenetics is important for monitoring patient response to treatment but is increasingly being replaced by the more sensitive and less invasive techniques of RT-PCR and FISH.

Treatment of patients with advanced chronic myelogenous leukemia with interferon-alpha-2b and continuous oral cytarabine ocfosfate (YNK01): a pilot study

The efficacy of continuous oral cytarabine ocfosfate (YNK01) (300 mg/day) in combination with interferon alpha (IFNalpha, 5x10(6) IU/day) was evaluated in patients with advanced chronic myelogenous leukemia, who previously failed to respond to IFNalpha-based therapies. Dose escalations up to 900 mg YNK01 were allowed in patients who failed to respond. In view of our results, four patients developed a complete hematological response after YNK01 was started. Among those who initially responded to YNK01, one complete cytogenetic response was achieved 18 months later. Although the data are preliminary, this is the first study showing that continuous administration of YNK01 along with IFNalpha is effective in patients with advanced chronic myelogenous leukemia.

Detection and quantification of residual disease in chronic myelogenous leukemia

The degree of tumor load reduction after therapy is an important prognostic factor for patients with CML. Conventional metaphase analysis has been considered to be the 'gold standard' for evaluating patient response to treatment but this technique normally requires bone marrow aspiration and is therefore invasive. The frequency of cytogenetic analyses can be considerably reduced if patients are also monitored by molecular methods, which can be performed on peripheral blood specimens. Of the various techniques available, most attention has been paid to RT-PCR for BCR-ABL mRNA since this is by far the most sensitive. Simple, non-quantitative RT-PCR analysis gives only limited information on patients after treatment. Quantitative RT-PCR assays have been developed to monitor the kinetics of residual BCR-ABL transcripts over time. Variables in the quantitative PCR assay may be controlled for by quantification of transcripts of a normal gene (eg ABL or glucose-6-phosphate dehydrogenase, G6PD) as an internal standard. After allogeneic stem cell transplantation, most patients become RT-PCR negative, often after a period of low level positivity that may persist for several months. Those patients destined to relapse are characterized by the reappearance and/or rising levels of BCR-ABL transcripts. In contrast, for patients treated with interferon-alpha (IFN) residual disease is rarely, if ever, eliminated. The actual level of minimal residual disease in complete cytogenetic responders to IFN correlates with the probability of relapse. New quantitative real time procedures promise to simplify the protocols that are currently in use, but standardization and the introduction of rigorous, internationally accepted controls are required to enable RT-PCR to become a robust and routine basis for therapeutic decisions.

Role of interferon-alpha and clonally expanded T cells in the immunotherapy of chronic myelogenous leukemia

Twenty five percent of patients in the chronic phase of chronic myelogenous leukemia (CML) are treated with interferon-alpha (IFN-alpha) to induce a cytogenic remission. In addition to its direct effects on leukemic cells, IFN-alpha has been shown to induce immunologic alterations, including upregulation of the expression of major histocompatibility (MHC) antigens in antigen-presenting cells (APCs), as well as augmentation of the activity of the lymphocytes against tumor cells. However, there has been little direct evidence supporting a causal interaction between cellular immunoreactivity and clinical responsiveness to IFN-alpha. We have shown that one approach to elucidate the immunological mechanisms by which IFN-alpha exerts its anti-CML activity is by analyzing therapy-induced modulation in T-cell receptor (TCR) Vbeta chain usage, using the reverse transcription-polymerase chain reaction (RT-PCR) followed by single-strand conformation (SSCP) analysis. This method is particularly attractive, since it provides an index of antigen-specific T cell expansion, but does not require the extraction and purification of the antigens involved in the T-cell response. T cell clones that express the Vbeta 10, 12, and 14 families predominate in the peripheral blood (PB) of CML patients. The enhanced expression of the Vbeta 9 and 20 families has been detected in IFN-alpha responsive patients but not patients who are poorly responsive to this agent. This suggests that expansion of T cells expressing these TCR Vbeta gene families may serve as a prognostic factors of the clinical responsiveness of CML patients to IFN-alpha. In addition, since T cell clones that express certain Vbeta families may react with a discrete set of antigenic peptides presented on the surface of malignant cells, a better understanding of the immunobiology of T cells in CML may allow for the design of increasing efficacious immune therapy for this disease.

Evidence from a leukaemia model for maintenance of vascular endothelium by bone-marrow-derived endothelial cells

BACKGROUND

Vascular endothelial cells lost from the blood-vessel endothelium through necrosis or apoptosis must be replaced. We investigated in a leukaemia model whether bone-marrow-derived endothelial cells contribute to this maintenance angiogenesis.

METHODS

We studied six patients with chronic myelogenous leukaemia (CML) carrying the BCR/ABL fusion gene in their bone-marrow-derived cells. We screened endothelial cells generated in vitro from bone-marrow-derived progenitor cells and vascular endothelium in myocardial tissue for the BCR/ABL fusion gene by in-situ hybridisation. For detection of donor-type endothelial cells after transplantation of haemopoietic stem cells, recipient tissue was stained with monoclonal antibodies against donor-type HLA antigens.

FINDINGS

We identified the BCR/ABL fusion gene in variable proportions (0-56%) of endothelial cells generated in vitro. Endothelial cells expressing the fusion gene were found in the vascular endothelium of a patient. In a recipient of an allogeneic stem-cell transplant, normal donor-type endothelial cells were detected in the vascular endothelium.

INTERPRETATION

These findings suggest that CML is not solely a haematological disease but originates from a bone-marrow-derived haemangioblastic precursor cell that can give rise to both blood cells and endothelial cells. Moreover, normal bone-marrow-derived endothelial cells can contribute to the maintenance of the blood vascular endothelium. The integration of bone-marrow-derived endothelial cells into the vascular endothelium provides a rationale for developing vascular targeting strategies in vasculopathies, inflammatory diseases, and cancer.

Fluorescence in situ hybridization on peripheral-blood specimens is a reliable method to evaluate cytogenetic response in chronic myeloid leukemia

PURPOSE

To evaluate the usefulness of fluorescence in situ hybridization (FISH) on peripheral-blood specimens to evaluate the cytogenetic response to treatment in patients with chronic myeloid leukemia (CML).

PATIENTS AND METHODS

In a first attempt, we analyzed 62 bone marrow specimens using interphase FISH and compared the results with those of conventional cytogenetics. In a second step, we analyzed 60 paired sets of bone marrow and peripheral-blood specimens with interphase FISH.

RESULTS

The results of interphase FISH agreed with conventional cytogenetics on bone marrow for most patients, and only minor differences were found (r =.98). The comparison of interphase FISH on bone marrow versus peripheral-blood specimens showed a strong correlation between these two specimen sources (r =.97).

CONCLUSION

Our results confirmed that FISH is a sensitive technique for the evaluation of response to treatment in patients with CML. Moreover, our study suggests that follow-up of cytogenetic response to therapy can be evaluated on peripheral-blood specimens, thus enabling an easier and more frequent evaluation of patients. The next step will be to evaluate this technique in a large prospective trial to define the prognostic value of complete remissions evaluated by FISH.

Minimal residual disease in hematologic disorders

In almost no other area of medical oncology has the introduction of new drugs, combinations of chemotherapeutic agents, and novel biologic treatments caused such dramatic responses as it has in the treatment of malignant hematologic disorders. However, despite some therapeutic success, many patients relapse and die from recurrence of their disease. The implications of minimal residual disease (MRD), a term referring to disease that is undetectable by conventional morphologic methods, have therefore attracted increasing attention in recent years. New and powerful laboratory tools such as polymerase chain reaction assays have extraordinary sensitivity and provide exciting new insights into the detection, nature, quantification, and kinetics of MRD. This article summarizes methods used in the identification of MRD and its importance as exemplified in the case of acute leukemias and chronic myelogenous leukemia.

Chronic myelogenous leukemia

Over the past year, new information has been reported on the biology and treatment of chronic myelogenous leukemia (CML). Chronic myelogenous leukemia is characterized by the breakpoint cluster region (BCR-ABL) chimeric gene, the product of which is p210BCR-ABL, a tyrosine kinase that gives hematopoietic cells the characteristics of excessive proliferation, resistance to physiologic apoptotic signals, and resistance to chemotherapy. Recently, investigators have attempted to 1) elucidate the mechanisms by which the BCR-ABL gene and its product initiate and maintain the malignant phenotype, 2) improve the use of the BCR-ABL gene as a diagnostic marker of disease, and 3) inhibit the expression of this gene as a therapeutic maneuver. Other investigators have tried to explain interferon's mechanism of action in the treatment of CML and to improve the safety and applicability of stem cell transplantation (SCT) as a therapy for CML.

A Special Fluorescent In Situ Hybridization Technique to Study Peripheral Blood and Assess the Effectiveness of Interferon Therapy in Chronic Myeloid Leukemia

Using a highly sensitive fluorescence in situ hybridization method with probes for BCR and ABL1 (D-FISH), we studied 37 paired sets of bone marrow and blood specimens, collected within 24 to 96 hours of each other, from 10 patients before and during treatment for chronic myeloid leukemia (CML). The normal range for 500 interphase nuclei was ≤4 (≤0.8%) nuclei based on 10 bone marrow and 10 blood specimens from normal individuals. The percentage of neoplastic nuclei was usually lower in blood than bone marrow. However, changes in the percentage of neoplastic nuclei in blood and bone marrow tracked closely over the course of therapy and with the results of quantitative cytogenetic studies on bone marrow. This result indicates that D-FISH is useful to test blood from patients with CML to monitor therapy. Moreover, by analysis of 6,000 nuclei with D-FISH, residual disease was identified in bone marrow and blood for patients in complete cytogenetic remission. Consequently, D-FISH analyses of interphase nuclei from blood could substitute for Q-cytogenetic studies on bone marrow. Thus, it may not be necessary to collect bone marrow samples so frequently to monitor therapy in CML.

A Special Fluorescent In Situ Hybridization Technique to Study Peripheral Blood and Assess the Effectiveness of Interferon Therapy in Chronic Myeloid Leukemia

Using a highly sensitive fluorescence in situ hybridization method with probes for BCR and ABL1 (D-FISH), we studied 37 paired sets of bone marrow and blood specimens, collected within 24 to 96 hours of each other, from 10 patients before and during treatment for chronic myeloid leukemia (CML). The normal range for 500 interphase nuclei was ≤4 (≤0.8%) nuclei based on 10 bone marrow and 10 blood specimens from normal individuals. The percentage of neoplastic nuclei was usually lower in blood than bone marrow. However, changes in the percentage of neoplastic nuclei in blood and bone marrow tracked closely over the course of therapy and with the results of quantitative cytogenetic studies on bone marrow. This result indicates that D-FISH is useful to test blood from patients with CML to monitor therapy. Moreover, by analysis of 6,000 nuclei with D-FISH, residual disease was identified in bone marrow and blood for patients in complete cytogenetic remission. Consequently, D-FISH analyses of interphase nuclei from blood could substitute for Q-cytogenetic studies on bone marrow. Thus, it may not be necessary to collect bone marrow samples so frequently to monitor therapy in CML.